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Modern “mild-hybrid” vehicles use a lithium-ion batteries to power systems that a 12-volt battery can’t handle alone.

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The battery pack feeds the belt-starter generator (or ISG) for smooth start-stop, torque assist (“torque-fill”), and regenerative braking. It also supports components like active suspension/roll control, electric superchargers/e-turbos, and then steps power down through a 12V DC-DC converter to stabilize the 12V network.

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Inside the pack, a Battery Management System (BMS) monitors cell voltage, temperature, current, State-of-Charge (SoC) and State-of-Health (SoH), performs cell balancing, controls contactors/pre-charge, and communicates with the vehicle over CAN. Many cars include safety elements such as pyro-disconnects that open in a crash event.

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When the battery pack degrades or the BMS flags a fault, you may see: disabled start-stop, loss of torque assist, DC-DC converter errors, charge warnings, random module resets, and a stack of DTCs. Because the battery system can deliver very high current, incorrect repairs risk thermal damage, arcing, and cascading electronic failures.

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Professional repair matters because proper recovery requires:

• Pack diagnostics (cell IR/capacity checks, balance status, thermal inspection)

• BMS service (fault analysis, coding/calibration, firmware where applicable)

• Contactor/pre-charge & sensor verification, wiring & interlock checks

• Bench validation under load and integration tests with the vehicle

Bottom line: a correctly repaired 48V Li-ion pack restores performance, reduces faults and downtime, protects 12V systems, and keeps the mild-hybrid features working as designed.